The Raspberry Pi is hardly the first ultra-compact PC to appear on the market, but its low cost and charitable status have certainly caught people's attention. The Pi is now, however, looking increasingly like the device which heralds an explosion in similar teeny-tiny gadgets from companies as diverse as a Bulgarian open-source hardware cooperative and chip giant Intel.

If you're not familiar with the Raspberry Pi, you've probably been asleep for a couple of years - in which case, let us be the first to welcome you to the world of tomorrow! While you were snoozing, a charitable foundation set up by a collection of hardware and software engineers and academics designed and launched a $35 ARM-based credit card-sized computer, with no lesser an aim than a revolution in computing education.

The Pi has fended off less flexible competition, such as the significantly more expensive BeagleBone, to capture the imaginations of hackers across the world. The Foundation is still struggling to meet demand for the device, despite entering into manufacturing agreements with electronics giants Farnell and RS Components.

The Pi might be the logical choice for an ultra-compact PC for now, but other companies are cognisant of the device's unparallelled success - and are unlikely to leave the market to the Foundation for long.

First up to offer some serious competition to the Pi is the OLINUXINO by Bulgarian open hardware giant Olimex. Unlike the Pi, the OLINUXINO is a totally open source design: once the product launches - with June suggested as a likely date - it will be possible for enthusiasts and companies to build their own, something the Pi's designers have yet to offer.

The OLINUXINO also boasts a few other improvements over the Pi's design: the board offers compatibility with 'shield' boards designed for the Arduino microcontroller, making it easy to add additional hardware to the device, and features noise immunity for industrial use. It also uses the readily available iMX233 microcontroller as its central processor, which can be purchased as an individual unit for those looking to build their own OLINUXINO by hand.

Olimex's Pi competitor does, however, fall down in the specification stakes: while the iMX233 boasts an ARM926J processor, it runs at a mere 454MHz to the Pi's 700MHz; it also lacks the high-performance VideoCore IV graphics hardware of the Pi's Broadcom BCM2835. The OLINUXINO also has a mere 64MB of RAM, and relies on a composite video connection with no sign of the Pi's high-resolution HDMI port.

Pricing is also against the OLINUXINO: while the Pi retails at £29, suggested pricing for Olimex's equivalent is £36.65 excluding tax - although a 'mini' version lacking Ethernet connectivity and comparable to the Pi's Model A variant will be available for £24.42.

For power users looking for something a step up, rather than a step down, from the Pi, Intel's NUC project is worth investigating. The Next Unit of Computing (NUC) design packs a desktop-class Ivy Bridge processor into a box not much bigger than a couple of Pis side-by-side.

If the Pi is the Model T of the ultra-compact computing revolution, Intel's NUC promises to be the Ferarri. The device is, however, aimed at a very different market: pricing will be north of £100 bare-bones and significantly more when you've bought the processor and memory, and the device relies upon a bulky laptop-style external power supply - a far cry from the Pi's micro-USB power input.

The high price and power draw mean that the Raspberry Pi Foundation has little to worry about from Intel's NUC project, but Intel's sudden interest in ultra-compact computing will likely have another victim: VIA. While the company still sells small quantities of its low-power x86 hardware, the 10x10cm form factor of Intel's NUC competes directly with the smallest of VIA's reference designs while offering significantly improved performance.

Although the OLINUXINO and NUC are hardly the only ultra-compact systems due for launch in the near future, they are two of the most interesting - and clear harbingers of a coming wave of teeny-tiny technology which could have as big an impact on the technology industry as did the microcomputing revolution of the 80s.